Method and device for producing post-stretched cellulose spun threads

ABSTRACT

The invention relates to a method and device for producing Lyocell fibres from a spinning solution containing water, cellulose and tertiary amine oxide. The spinning solution is extruded to form spun threads ( 10 ). The spun threads ( 10 ) are stretched and passed through a precipitation bath ( 16 ) in order to precipitate the cellulose. It has been surprisingly revealed that the tenacity of the Lyocell fibres produced in this way can be increased when the stretched fibres are subjected to post-stretching in a post-stretching means. The post-stretched Lyocell fibres have a wet modulus of at least 260 cN/tex.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Application No. PCT/EP2004/001268 filed Feb. 11, 2004, which claims priority to German Application No. 103 14 878.7 filed on Apr. 1, 2003. Priority to each of these applications is hereby claimed. The subject matter of each of these applications is also hereby incorporated by reference.

BACKGROUND OF THE INVENTION

The invention relates to a method for the production of Lyocell threads from a spinning solution containing water, cellulose and tertiary amine oxide as well as the spun threads produced by this method.

Furthermore, the invention relates to a device for the manufacture of spun threads from a spinning solution containing cellulose, water and tertiary amine oxide, with a spinneret, through which the spinning solution can be extruded in operation to form spun threads, with a precipitation bath with a precipitating agent to precipitate cellulose, through which the spinning threads are passed in operation, with a first stretching means, through which the spun threads can be stretched in operation, and with a second stretching means, through which the spun threads stretched by the first stretching means can be post-stretched in operation, and with a heating device arranged in the region of the second stretching means and by which the spun threads can be heated in operation during the post-stretching.

With the manufacturing method the spinning solution is first extruded to spun threads, then the spun threads are stretched and passed through a precipitation bath, and thereafter the cellulose of the spun threads coagulates.

The method of producing spun threads (in the following the terms “fibres” and “threads” are used synonymously) from cellulose dissolved in a tertiary amine oxide such as N-methyl-morpholine-N-oxide and water, also termed the Lyocell method, goes back to the patent specifications U.S. Pat. No. 4,142,913, U.S. Pat. No. 4,144,080, U.S. Pat. No. 4,211,574, U.S. Pat. No. 4,246,221, U.S. Pat. No. 4,261,943 and U.S. Pat. No. 4,416,698. In these patent publications, attributable to McCorsley, the fundamental principle of the production of Lyocell fibres with the three process steps of extruding the spinning solution to spun threads in an air gap, stretching of the extruded spun threads in the air gap and precipitation of the cellulose in a precipitation bath was first described.

After the precipitation and coagulation of the cellulose, the spun threads can be passed on for further processing steps. Thus, the spun threads can be washed, dried and treated or impregnated with additives. The spun threads can be cut for the production of staple fibres.

The advantage of the Lyocell method lies in the good environmental compatibility and in the excellent mechanical properties of the spun threads or fibres. Through various further developments of the method developed by McCorsley the efficiency could be significantly improved.

The Lyocell fibres differ with regard to their structure and their textile properties and in their manufacture from the other cellulose fibres, such as described, for example, in DE-A-100 16 307, WO-A-01/58960, DE-A-197 53 806, DE-A-197 21 609, DE-A-195 11 151 and DE-A-43 12 219.

A special problem of the Lyocell method compared to the methods described there lies in the high surface adhesion of the freshly extruded spun threads. When the spun threads touch one another in the air gap, they stick together, which either leads to an unsatisfactory fibre quality or even to an interruption in the spinning process and to a restart of spinning. As described in DE-A-284 41 63, McCorsley used the spun threads in the air gap via a roll with a precipitation bath solution. This arrangement is however not practical at high spinning speeds. A series of further developments of the McCorsley method therefore involves measures to reduce the surface adhesion of the spun threads in the air gap and to improve the operational reliability, also known as the spinning reliability, of the production method.

One measure, which is widespread in the state of the art in the production of Lyocell fibres or spun threads, is to blow with a cooling gas onto the spun threads in the air gap in order to cool the surface of the freshly extruded spun threads and to lower their adhesion. This type of cooling blowing is for example described in WO-A-93-9230, WO-A-94 2818, WO-A-95 01470 and in WO-A-95 01473. According to these publications, various types and embodiments of ventilation are used depending on the arrangement of the extrusion openings through which the spinning solution is extruded.

A further problem in the production of Lyocell fibres is the design of the precipitation bath. Due to the high extrusion speed the spun threads are dipped into the precipitation bath solution at a high speed and carry along the surrounding precipitation bath solution. Consequently, a flow is generated in the precipitation bath, which churns up the surface of the precipitation bath and mechanically stresses the spun threads to the point of tearing them when dipping into the precipitation bath.

In order to keep the surface of the precipitation bath as calm as possible with extrusion openings arranged in an annular shape, in DE-A-1 00 60 877 and DE-A-1 00 60 879 the spun threads are passed through specially designed spinning funnels filled with the precipitation bath. With the spinning funnels the precipitation bath solution flows out together with the spun threads at the lower end. This stream driven by the force of gravity can, as described in DE-A-44 09 609, be exploited for stretching the spun threads.

With extrusion openings arranged on a rectangular area, according to DE-A-100 37 923 good results have been achieved when the spun threads form an essentially flat curtain and are deflected to the precipitation bath surface as a flat curtain in the precipitation bath. A deflection element is arranged in the precipitation bath in this design.

The further processing of Lyocell fibres after the extrusion and coagulation of the cellulose for obtaining certain mechanical properties of the spun threads is less well documented in the patent literature.

In the basic article “Was ist neu an den neuen Fasern der Gattung Lyocell?” (What is new in the new fibres of the Lyocell type?), Lenzinger Berichte (Lenzinger Reports) 9/94, pgs. 37-40, it is assumed that the fibre structure and the fibre properties are determined by the molecular alignment during the extrusion and the stretching which directly follows the extrusion. Here, the Lyocell fibres differ crucially from the fibres as they are described in DE-A-197 53 806, DE-A-197 21 609, DE-A-195 11 151, DE-A-100 16 307 and DE-A43 12 219.

This topic is taken up in the new patent literature and has been implemented in practice. Thus, in EP-A-823 945, EP-A-853 146 and DE-A-100 23 391 devices are described in which, after post-stretching of the extruded spun threads and after the coagulation of the cellulose in the stretched spun threads, they are maintained free of tensile stress during the further processing. These developments are based on the idea that the mechanical properties of the stretched and coagulated spun threads can no longer be modified.

One way that initially appears to go in the opposite direction is put forward only in EP-A-494 851. In this publication a method is described in which the essentially stress-free extruded and coagulated cellulose is stretched. The essential point in this method is that no stretching of the freshly extruded spun threads occurs. Through this method of EP-A494 851, which is unusual for Lyocell processing and which has apparently also not been developed further, a retrospective shaping of the spun threads is possible. The method of EP-A-494 851 is therefore similar to a plastic deformation process, whereby the starting material, the unstretched Lyocell threads, exhibits a rubbery consistency. The mechanical properties of the fibres produced according to the method of EP-A-494 851 are however not commensurate with present-day requirements.

In DE-A-102 23 268 it is described that a multi-stage precipitation and at the same time a multi-stage stretching of the spun threads can be realised if the wetting device is applied simultaneously to the stretching of the spun threads. With this measure the requirement on treatment medium is reduced and the control of the precipitation process is improved, but the textile properties are essentially unaffected by this type of retrospective stretching.

In JP-A-03-076822 a method of producing fire-resistant fibres is described. After coagulation of the unstretched fibres, the filaments are stretched for the first time, then oil is applied and they are dried. Then the filaments are post-stretched under steam and dried again.

For modifying the mechanical properties, such as the loop strength, tendency to fibrillation and tensile strength of Lyocell fibres, currently essentially the repertoire is taken up, as described in the article “Strukturbildung von Cellulosefasern aus Aminoxidlösungen” (Structure formation of cellulose fibres from amine oxide solutions), Lenzinger Berichte (Lenzinger Reports) 9/94, pgs. 31-35. Accordingly, the textile-related physical properties of Lyocell fibres are set by modifying the cellulose concentration in the spinning solution (cf. WO-A-96 18760), by variation of the draw-off conditions (cf. DE-A42 19 658) and the use of additives (cf. DE-A44 26 966, DE-A-218 121, WO-A-94 20656) as well as by modifying the precipitation conditions (cf. AT-B-395 724). All of these methods however only permit an indirect control of the mechanical properties of the Lyocell fibres or spun threads which in the process management is very inaccurate.

SUMMARY OF THE INVENTION

The object of the invention is therefore to improve the known methods and devices for the manufacture of Lyocell fibres such that the mechanical properties such as loop strength and the tensile strength of the Lyocell fibres can be selectively influenced by a process which is easy to control.

This object is solved for the manufacturing method mentioned in the introduction in that the stretched spun threads are post-stretched and simultaneously heat treated.

For the device mentioned in the introduction this object is solved in that the spun threads can be stretched by the first stretching means in an air gap before entering the precipitation bath.

Surprisingly, the mechanical properties—here in particular the wet modulus—compared to the conventional Lyocell fibres can be substantially improved by the post-stretching or elongation of the spun threads which have already been stretched in the air gap and then been coagulated. Due to the heat treatment during the post-stretching, according to initial tests, the wet modulus is slightly reduced and the fibre again becomes slightly more elastic.

In contrast to the method and device of DE-A-102 23 268 the heat treatment carried out during the post-stretching facilitates a decisive improvement of the textile properties of the Lyocell fibres.

Thus, Lyocell fibres produced with the method according to the invention can achieve a wet modulus of at least 250 cN/tex and a wet abrasion number per 25 fibres of at least 18. With the method according to the invention wet modulus figures of at least 300 cN/tex or 350 cN/tex can be achieved. The wet maximum tensile force elongation can here assume relatively low values, for example at the most 12%.

Generally, higher figures for the wet modulus arise if the spun threads are coagulated before the post-stretching.

The heat treatment can be carried out as a drying process in a stage following a washing or impregnation process, i.e. so-called stress drying. Alternatively, the heat treatment can take place in a steam or dry steam atmosphere. The steam or dry steam can contain impregnation agents which act on the spun threads and lead to a chemical secondary treatment.

Preferably the heat treatment is carried out in an oven in which the stretched and coagulated spun threads are post-stretched with a specified tensile stress between two godets. Here, a hot inert gas, such as hot air, or steam or dry steam can be passed through the surfaces of the galettes and the spun threads lying on them.

After the post-stretching the spun threads can be crimped, since the natural crimping of the spun threads is significantly reduced due to the post-stretching. Here, treatment with dry steam at the same time as crimping is also possible.

Finally, the spun threads can be cut for the manufacture of staple fibres.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following the invention is explained in more detail based on an embodiment and based on experimental results and experimental examples with reference to the drawings.

The following are shown:

FIG. 1 a schematic overview of a system for the manufacture of post-stretched Lyocell fibres;

FIG. 2 an embodiment of a means of post-stretching in a schematic view;

FIG. 3 a further embodiment of a means of post-stretching in a schematic view.

DETAILED DESCRIPTION

First, the basic structure of a system 1 for the manufacture of Lyocell fibres is described based on the schematic representation of FIG. 1. The system 1 of FIG. 1 is used for the manufacture of staple fibres of Lyocell.

A highly viscous spinning solution containing water, cellulose and tertiary amine oxide, for example N-methyl-morpholine-N-oxide is passed through a pipe system 2. The pipe system 2 is constructed in a modular manner from fluid pipe sections 2 a of a certain length, which are joined together via standard flanges 2 b.

The fluid pipe sections 2 a are provided with an interior temperature stabilisation device 3, which is fitted in the fluid pipe sections 2 at the point of the core flow of the spinning solution and through which the temperature of the spinning solution in the pipe system 2 is closed-loop controlled.

A temperature controlled fluid is passed via feed modules 4 arranged between two adjacent fluid pipe sections through the interior temperature stabilisation device, as indicated by the arrows 5. The feed modules 4 essentially exhibit the dimension of the standard flanges and can be fitted with such flanges for connection.

At certain distances, burst modules 6, likewise arranged between the fluid pipe sections 2 a, are substituted for the feed modules 4. The burst modules 6 essentially exhibit the same design as the feed modules 4. They are fitted with burst elements which are not shown in FIG. 1 and which burst when a certain pressure is exceeded in the pipe system 2, permitting an outwards diversion of pressure. Bursting can in particular occur during a spontaneous exothermic reaction of the spinning solution due to over-ageing or over-heating. The spinning solution emitted outwards during the burst is caught in the collection containers 7, from where it can be recycled or removed.

The spinning solution is passed to a spinning head 8 through the pipe system 2. The spinning head 8 is fitted with a spinneret 9 which comprises a large number of extrusion openings (not illustrated), normally many thousands of extrusion openings. The spinning solution is extruded to spun threads 10 through the extrusion openings. The arrangement of the extrusion openings in the spinneret 9 can be of circular, annular or rectangular shape; in the following reference is made only to a rectangular arrangement as an example.

In order that optimum spinning conditions prevail at the extrusion openings, apart from the temperature stabilisation device 3 in the pipe system 2, further installed devices can be provided which similarly can be easily joined to the fluid pipe sections 2 a or to the feed modules 4 or burst modules 6 via the standard flanges. Thus, a pressure equalisation container 11 a can be arranged in the pipe system 2 to compensate for pressure variations and volume flow variations in the spinning solution in the pipe system 2 by changing its internal volume, ensuring a constant extrusion pressure at the extrusion openings of the spinning head 8.

Furthermore, a mechanical filter device 11 b with a back-purgable filter element (not shown) can be provided in the pipe system 2. The filter element exhibits a fineness between 5 μm and 25 μm. Due to the filter device 11 b a continuous or—when using alternate operating buffer storage vessels (not illustrated)—a discontinuous filtering of the spinning solution occurs.

The extrusion openings border on an air gap 12 through which the freshly extruded spun threads 10 pass and in which the spun threads are stretched by tensile stress. In the air gap 12 a cooling gas flow 13, produced by a blower device 14, is directed onto the spun threads 10. The temperature, moisture and composition of the cooling gas flow 13 can be controlled to predetermined or variable specified values by a climatic device 15.

The cooling gas flow 13 acts at a distance from the spinneret 9 on the spun threads 10 and exhibits a velocity component in the extrusion direction E so that the spun threads are stretched by the cooling gas flow 13. To facilitate good heat transport the cooling gas flow 13 is turbulent.

After crossing the air gap 12, the spun threads 10 enter a precipitation bath 16. In order to avoid churning up the surface of the precipitation bath 16, the cooling gas flow 13 is spaced sufficiently from the surface 17 of the precipitation bath, so that it does not impinge on the surface.

In the precipitation bath 16 the spun threads 10 are deflected by an essentially roll-shaped deflector 18 to a bundle unit 19 outside the precipitation bath, so that they again pass through the surface 17 of the precipitation bath. The deflector or diverter can be configured rigidly or fixed or it can rotate with the spun threads. The bundle unit 19 is rotary driven and as the first means of stretching exerts a tensile stress, acting back up to the extrusion openings of the spinneret 9, via the diverter 18 onto the spun threads 10, which stretches the spun threads. Of course, the diverter 18 can also be driven as a means of stretching.

In order to stretch the spun threads 10 as gently as possible, the tensile stress can also be produced solely by the cooling gas flow 13 as the first means of stretching. This has the advantage that the tensile stress is transferred into the spun threads 10 by a frictional stress acting distributed over the surface of the spun threads.

From the bundle unit 19 the spun threads 10 are combined to a spun thread bundle 20. Then, the spun threads 10, still wet with the precipitation bath solution 16 and combined to a spun thread bundle 20, are laid free of stress on a conveyor device 21 and transported on it largely free of tensile stress. During the transport of the spun threads on the conveyor device 21 the complete or almost complete coagulation of the cellulose of the spun threads takes place with as little effect from stress as possible.

The conveyor device 21 can, as shown in FIG. 1, be configured as a vibroconveyor, which transports the spun thread bundle 20, or optionally a number of spun thread bundles 20 simultaneously, by vibrations in the conveying direction F. The vibrations of the conveyor device 21 are indicated by the double arrow 22. Due to the to and fro movement 21 the bundle of spun threads 20 is placed in order on the conveyor device. Instead of the vibroconveyor 22 other conveying devices such as a number of consecutively arranged godets can be used with a circumferential speed which is almost constant or which reduces in the conveying direction.

During the transport on the conveying device 21 various treatments of the spun thread bundle 20 can occur, for example the spun thread bundle 20 can be washed once or many times, dried and brightened, for example by a sprinkling system 23 from which a treatment medium 24 is sprayed onto the spun thread bundle 20.

The spun thread bundle 20 is taken up by a godet 25 from the conveyor device 21 and passed to a second post-stretching unit 26 through which the thoroughly coagulated spun threads 10 are post-stretched.

In the embodiment of FIG. 1 the post-stretching takes place during simultaneous heat treatment or drying in the form of stress drying, because in this way the mechanical properties of the spun threads 10 are most favourably influenced. Slightly worse properties, which however are still excellent compared to the state of the art, are obtained when the heat treatment during the post-stretching is omitted.

The second post-stretching means 26 can also be provided immediately after the bundling unit 19, i.e. between the conveyor device 21 and the precipitation bath 16, so that first the post-stretched spun threads are subjected to further treatment steps.

For carrying out the heat treatment, the post-stretching means 26 in the entry section of the spun thread 20 can comprise a heating device 27 which brings the spun thread bundle 20 to a certain temperature and at the same time dries the spun thread bundle 20 at least on the surface.

In the post-stretching means 26 the spun threads are passed over two godets 28, 29, which are driven such that the spun thread bundle 20 is subjected to a predetermined post-stretching tensile stress Z_(N) between them. The spun thread bundle subjected to this tensile stress is maintained at a specified high temperature and during the post-stretching can be impregnated in particular with a hot inert gas, such as air, or by steam, for example dry steam and with swelling agents or other agents for chemical fibre treatment, as indicated by the arrows 30. The godets 28, 29 can also be heated to support the drying effect.

Due to the post-stretching, the spun thread bundle 20 exhibits reduced crimping compared to conventional fibres so that it is crimped via a stuffer box 31. Then, the spun thread bundle 20 is cut by a cutting device 32. If an endless fibre is to be produced, the crimping and/or cutting can of course be omitted.

After crimping and cutting the crimped staple fibres can be transported in random orientation in the form of a crimped endless cable 33 on a conveyor device 34 to further process steps.

FIG. 2 shows schematically an embodiment of a post-stretching means 26. With this embodiment post-stretching in the form of stress drying occurs.

As already described for FIG. 1, the post-stretching means 26 comprises two godets 28, 29 which are driven such that the spun thread bundle 20 is tensioned or extended between them with a predetermined tensile stress Z_(N) of at least 0.8 cN/tex, preferably at least 3.5 cN/tex. In this respect, the godet 29 following in the conveying direction F can be rotated at a predetermined higher speed than the godet 28 preceding in the conveying direction F, whereby a slippage, essentially determining the tensile stress Z_(N), can prevail between the godet 29 and the spun thread bundle 20 looped around the galette.

The shrinkage of the spun thread bundle 20 during drying can also be exploited for stretching it: Since the spun thread bundle shortens during the drying process, an elongation or post-stretching also then takes place if this shortening is not compensated by the rotational speed of the godets 28, 29. In this way post-stretching can also occur when the galettes 28, 29 rotate with essentially the same or only slightly different speeds.

One or both godets 28, 29 can be provided with a surface 30 which is at least permeable to gas and through which a hot inert gas, steam or dry steam is pressed from the interior space of the godets 28, 29 through the spun thread bundle 20 looped around the godets 28, 29.

Alternatively or in addition to looping as illustrated in FIG. 2, a roll 28 a, 29 a, also permeable to steam and actively or passively rotating with the godet, can be arranged in a position opposite each godet 28, 29, as schematically illustrated in FIG. 3. The rolls 28 a, 29 a, also exhibit permeable surfaces through which the inert gas or steam is drawn off. Large drums can also be provided instead of rolls.

Instead of the godets 28, 29 also larger drums or suction drums with a perforated surface can be used through which the hot gas is drawn off.

In the region between the godets 28, 29 hot air or another inert hot gas, steam or dry steam is passed through gas or the spun thread bundles 20. The effectiveness of the post-stretching has been proven in a series of tests.

The tests were carried out on a spun thread bundle of 79,270 single spun threads and a total titre of 110,978 dtex, corresponding to a single titre of 1.4 dtex. Table I gives an overview of the test results.

In a first series of tests (Tests 1 to 7) the spun thread bundle was dried at 73° C. over 15 min. under various conditions.

In Test 1 the spun thread bundle was dried without tension.

In Test 2 the spun thread bundle was dried without tension, moistened again and dried under tension. To do this, the spun thread bundle was passed through two eyes at a distance of 50 cm and loaded at each end during drying with 19 kg.

In Test 3 the spun thread bundle was dried without tension, moistened again and dried under tension. To do this, the spun thread bundle was passed through two eyes at a distance of 50 cm and loaded at each end during drying with 38 kg.

In Test 4 the spun thread bundle was clamped between two clamps at a distance of 38 cm and then dried.

In Test 5 the moist spun thread bundle was dried under tension. The spun thread bundle was passed through two eyes at a distance of 50 cm and loaded at each end with a weight of 9 kg.

In Test 6 the moist spun thread bundle was dried under tension. The spun thread bundle was passed through two eyes at a distance of 50 cm and loaded at each end with a weight of 19 kg.

In Test 7 the moist spun thread bundle was dried under tension. The spun thread bundle was passed through two eyes at a distance of 50 cm and loaded at each end with a weight of 38 kg.

In a second series of tests the spun thread bundle was subjected to treatment with caustic soda solution (NaOH) before the drying. First, the spun thread bundle was treated with a 5% NaOH solution for 5 min. and then washed with fully deionised water. The NaOH solution was neutralised with 1% formic acid and again washed with fully deionised water.

The spun thread bundle was then dried in the dryer at 73° C. for 30 min.

In Test 8 the spun thread bundle was dried without tension.

In Test 9 the spun thread bundle was dried without tension, moistened again and dried under tension. To do this, the spun thread bundle was passed through two eyes at a distance of 50 cm and loaded at each end with 19 kg.

In Test 10 the spun thread bundle was dried without tension, moistened again and dried under tension. To do this, the spun thread bundle was passed through two eyes at a distance of 50 cm and loaded at each end with 38 kg.

In Test 11 the spun thread bundle was clamped between two clamps at a distance of 38 cm and then dried.

In Test 12 the moist spun thread bundle was dried under tension. The spun thread bundle was passed through two eyes at a distance of 50 cm and loaded at each end with a weight of 9 kg.

In Test 13 the moist spun thread bundle was dried under tension. The spun thread bundle was passed through two eyes at a distance of 50 cm and loaded at each end with a weight of 19 kg.

In Test 14 the moist spun thread bundle was dried under tension. The spun thread bundle was passed through two eyes at a distance of 50 cm and loaded at each end with a weight of 38 kg.

With the dried spun thread bundles the titre, the denier related maximum tensile force, maximum tensile force elongation, denier related wet maximum tensile force, wet maximum tensile force strain, denier related loop maximum tensile force, the wet modulus and the wet abrasion number were then determined. In doing this the following test specifications were followed.

The titre was determined according to DIN EN ISO 1973. The (wet) maximum tensile force and the (wet) maximum tensile force elongation were determined according to DIN EN ISO 5079. The loop maximum tensile force was determined according to DIN 53843 Part 2.

The wet modulus was determined on a fibre bundle which can be used according to DIN EN 1973. The procedure followed the test specification ASG N 211 from Alceru Schwarza GmbH. The tests for the determination of the wet modulus were carried out on a tensile testing machine with constant rate of elongation and low-displacement electronic force measurement. The clamping length of the fibre bundle was 10.0 mm±0.1 mm. The denier related pretension force for a titre of over 2.4 dtex was 2.5 mN/tex±0.5 mN/tex. With a titre up to 2.4 dtex a pretension mass of 50 mg was used. The rate of strain was 2.5 mm/min with a mean wet elongation at tear of up to 10%, 5.0 mm/min with a mean wet elongation at tear of over 10 to 20% and 7.5 mm/min with a mean wet elongation at tear of over 20%.

Five spun thread bundles were placed into a flat dish with wetting agent solution for at least 10 s, whereby previously the pretension mass was clamped on one end of each spun thread bundle. The test sample placed in for respectively the longest time was removed from the dish and used for the tensile test and after each test a new test sample was to be placed in the dish for wetting.

The spun thread bundle to be clamped was clamped with its end opposite the pretension mass in the tensile testing machine while the pretension took effect and then the lower clamp was closed and the dip tank with the wetting agent solution was raised so that the liquid level reached as far as possible to the upper clamp without however touching it. The distance between the clamps must be continuously increased at the above stated strain rate until a strain rate of 5% is obtained. At this point the movement of the lower clamp was stopped and the wet tensile force determined in mN to one decimal place.

The wet modulus M is calculated from the arithmetic mean of the wet tensile force F in millinewtons and the mean denier T in tex calculated for the tested spun fibres and stated in millinewtons per tex rounded off to integers: M=F/(T·0.05).

The wet abrasion number was determined with a fibre wet abrasion testing device FNP from SMK Präzisionsmechanik Gera GmbH. The wet abrasion number is the number of revolutions of the abrasive shaft up to fracture of the fibre clamped under defined pretension in the wet abrasion test device. The pretension weight for a titre between 1.2 to 1.8 dtex was 70 mg. The rotational speed of the abrasive shaft was 400 rpm, the angle of contact 45°. The abrasive shaft is fitted with a textile tube.

From the tests according to Table 1 a surprising increase in the wet modulus as well as in the wet abrasion number of the post-stretched fibres can be seen compared to the conventional fibres which were not post-stretched (Test 1). With stress-free dried spun thread bundles, which were then moistened again and dried under tension (Tests 2, 3 and 9, 10), at the loading with 38 kg (corresponds to 3.12 cN/tex) compared to the loading with 19 kg (corresponding to 1.6 cN/tex), an increase in the wet modulus occurred with a slight drop in the wet abrasion number. With the heavier loading higher wet moduli can be obtained than with the moist fibre bundles that were dried under tension in the Tests 5 to 7 and 12 to 14.

The maximum tensile force, measured both wet and dry, is essentially unchanged compared to the fibres after Test 1, which were not post-stretched. It can be concluded from the reduced maximum tensile force elongation and the reduced loop maximum tensile force in conjunction with the wet modulus and the wet abrasion number that the post-stretched fibres are more brittle and ductile than the fibres which have not been post-stretched.

Therefore, the tests show that fibres with an improved wet modulus and an improved wet abrasion number can be produced by post-stretching or by stress drying. TABLE 1 Denier rel. Denier rel. wet max. tensile max. tensile Denier rel. loop Wet Wet abrasion Titre force Max. tensile force Wet max. tensile max. tensile force modulus number/25 dtex cN/tex force elongation % cN/tex force elongation % cN/tex cN/tex fibres Test 1 1.378 42.1 11.5 33.4 12.2 11.8 244 22 Test 2 1.450 43.2 9.7 32.9 11.2 7.3 272 48 Test 3 1.379 46.2 8.7 38.8 11.7 5.5 366 42 Test 4 1.420 43.6 10.5 29.3 11.8 11.9 308 34 Test 5 1.538 42.3 10.1 32.5 11.6 9.3 260 56 Test 6 1.423 42.3 10.0 32.5 12.4 7.7 288 38 Test 7 1.434 42.2 10.8 31.7 11.7 7.5 286 31 Test 8 1.390 39.4 10.6 31.8 12.4 9.6 258 23 Test 9 1.415 41.3 9.5 30.5 10.6 4.5 308 48 Test 10 1.436 40.4 8.6 33.4 11.2 5.0 346 35 Test 11 1.441 42.3 10.4 31.0 12.9 11.9 278 47 Test 12 1.369 42.6 9.7 27.8 11.0 8.8 294 39 Test 13 1.425 41.2 8.5 33.4 10.7 6.7 356 38 Test 14 1.381 42.1 9.3 28.0 9.5 5.6 334 40 

1. Method for the production of Lyocell fibres from a spinning solution containing water, cellulose and tertiary amine oxide, the method comprising: extrusion of the spinning solution to spun threads; stretching of the spun threads; passage of the spun threads through a precipitation bath; and post-stretching and simultaneous heat treatment of the stretched spun threads after passage through the precipitation bath.
 2. Method according to claim 1, further comprising: coagulation of the cellulose of the spun threads before stretching.
 3. Method according to claim 1, further comprising: post-stretching with a tensile stress of at least 0.8 cN/tex.
 4. Method according to claim 3, further comprising: post-stretching with a tensile stress of at least 3.5 cN/tex.
 5. Method according to claim 1, further comprising: treatment of the spun threads during heat treatment with hot inert gas.
 6. Method according to claim 1, further comprising: treatment of the spun threads during heat treatment with steam.
 7. Method according to claim 1, further comprising: passage of the spun threads through an air gap before the precipitation bath.
 8. Method according to claim 7, further comprising: blowing of the spun threads in the air gap with a flow of cooling gas.
 9. Method according to claim 1, further comprising: conveyance of the spun threads free of tensile stress between the stretching and the post-stretching.
 10. Method according to claim 1, further comprising: crimping of the post-stretched spun threads.
 11. Method according to claim 1, further comprising: cutting of the post-stretched spun threads to form staple fibres.
 12. Device (1) for the manufacture of spun threads from a spinning solution containing cellulose, water and a tertiary amine oxide, with a spinneret, through which the spinning solution can be extruded in operation to form spun threads, with a precipitation bath with a precipitating agent to precipitate cellulose, through which the spinning threads are passed in operation, with a first stretching means, through which the spun threads can be stretched in operation, and with a second stretching means, through which the spun threads stretched by the first stretching means can be post-stretched in operation, and a heating device arranged in the region of the second stretching means and by which the spun threads can be heated in operation during the post-stretching, wherein the spun threads can be stretched by the first stretching means in an air gap before entering the precipitation bath.
 13. Lyocell fibre, in particular manufactured by the method according to claim 1, wherein a wet modulus of at least 250 cN/tex and by a wet abrasion number per 25 fibres of at least
 18. 14. Lyocell fibre according to claim 13, wherein a wet modulus of at least 300 cN/tex.
 15. Lyocell fibre according to claim 14, wherein a wet modulus of at least 350 cN/tex.
 16. Cellulose fibres according to claim 13, wherein a wet tensile force elongation of at the most 12%.
 17. Cellulose fibres according to claim 13, wherein a wet abrasion number per 25 fibres of at the most
 25. 